The present invention relates to an optical disc apparatus which applies a light spot to an optical disc, thereby to record or reproduce information.
In recent years, optical disc apparatuses which applies a light spot to an optical disc thereby to record or reproduce information, such as a CD (Compact Disc) or MD (Mini Disc) have been developed. The optical disc has tracks on/from which the information is recorded/reproduced and the optical disc apparatus records/reproduces the information by making the light spot follow the tracks. The tracks are arranged concentrically or helically at intervals of several micrometers (1.6 xcexcm in the case of CD or MD) in its radial direction. The optical disc apparatus has light spot moving means for moving the light spot in a radial direction of the optical disc at high speed and with high precision, to follow these microscopic tracks. As examples of the light spot moving means, a tracking actuator for radially moving an objective lens which focuses a light spot, and a galvanomirror for changing an angle of an incident light to the objective lens are cited. However, only with such light spot moving means, a movement range of the light spot is limited by the size of the tracking actuator or the objective lens or the like and accordingly the movement range is small. Therefore, the optical disc apparatus usually includes traverse moving means for radially moving an optical head itself which internally contains the objective lens. Generally, control for making the light spot follow the tracks by using the light spot moving means is called xe2x80x9ctracking controlxe2x80x9d and control for making the optical head follow the movement of the light spot by using the traverse moving means is called xe2x80x9ctraverse controlxe2x80x9d.
In addition, in the conventional traverse control, a difference between the objective lens position and the center of the optical head is generated as an error signal, thereby to perform the control by using this error signal. A method in which a low-band component of a tracking driving signal supplied to the tracking actuator is used as the error signal is widely adopted. The low-band component of the tracking driving signal shows displacement of the objective lens by the tracking control, on the basis of a position where weight and gravity of the objective lens is balanced. When the moving direction of the tracking actuator is horizontal, it is a signal corresponding to a relative position of the objective lens and the center of the optical head, because the displacement of the objective lens by the gravity from the operation center of the tracking actuator in contrast to the moving direction of the tracking actuator is approximately xe2x80x9c0xe2x80x9d in this case. However, when the position of the apparatus is set up so as to have a vertical moving direction of the tracking actuator, i.e., when the optical disc apparatus is positioned xe2x80x9clongitudinally (vertically)xe2x80x9d, the objective lens is displaced downwardly due to its weight, which is referred to as xe2x80x9cself-weight dislocationxe2x80x9d. The position of the objective lens displaced due to the self-weight dislocation is the position where the weight and gravity of the objective lens is balanced, and the traverse control is executed with this position as a center. Therefore, in the conventional optical disc apparatus, when the self-weight dislocation occurs, the movable range of the tracking actuator is narrowed accordingly, whereby the follow-up characteristics of the tracking control are deteriorated.
Japanese Published Patent Application No.Hei.9-223320 discloses an optical disc apparatus which solves such problems. The optical disc apparatus disclosed therein comprises spot position signal generation means for generating a spot position signal which indicates relative displacement of a light receiving element in the optical head and a light spot, and has a structure of using the spot position signal as an error signal of the traverse control. According to this structure, the traverse control of this optical disc apparatus has a point where the spot position signal is zero as a control target and moves the optical head such that the light spot is positioned at the center of the light receiving element. In constituting the optical head, the center of the light receiving element and the operation center of the tracking actuator are previously arranged so as to coincide with each other. Therefore, the objective lens is always moved around the operation center of the tracking actuator, thereby avoiding the deterioration of the follow-up characteristics of the tracking control.
However, so constructed optical disc apparatus has a problem in stability of the operation at the starting of the operation of the traverse control means. FIG. 14 is a waveform chart showing waveforms of a spot position signal and a traverse driving signal in the conventional optical disc apparatus when theself-weight dislocation occurs. In FIG. 14, at an operation start time 1301 of the traverse control means, the objective lens is displaced due to the self-weight dislocation and the spot position signal has a large value A. When the spot position signal is input to the traverse control means in such a state to start the traverse control, a driving signal 1302 applied to a traverse motor has a high amplitude and becomes oscillatory. In the worst case, when the optical head is moved by the traverse motor, the tracking control is taken off. This is because the frequency band of the traverse control is usually limited to several Hertz or less so as not to follow the eccentricity, the traverse motor has large inertia and it is difficult to be moved or stopped, and the like.
It is an object of the present invention to provide an optical disc apparatus which allows operation of traverse control means by a spot position signal, even when the self-weight dislocation of an objective lens occurs due to variation in the position of the optical disc apparatus.
Other objects and advantages of the present invention will become apparent from the detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit and scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a 1st aspect of the present invention, an optical disc apparatus which applies a light spot to an optical disc, thereby to record or reproduce information on or from the optical disc, comprises: first moving means for moving the light spot applied to the optical disc, in a radial direction of the optical disc; an optical head having converging means for converging the light spot on the optical disc; spot position detection means for generating a spot position signal which indicates a positional difference in a radial direction of the optical disc, between a center of the optical head and the light spot on the optical head; first control means for subjecting the spot position signal to a first processing by a spot position loop filter, and outputting the spot position signal to the first moving means; second moving means for moving the optical head in a radial direction of the optical disc; second control means for subjecting the spot position signal to a second processing by a traverse loop filter, and outputting the spot position signal to the second moving means; and system operation control means for operating the first control means, and thereafter operating the second control means. Therefore, even when the self-weight dislocation occurs in the objective lens, the traverse control using the spot position signal can be performed with stability, thereby realizing an optical disc apparatus which is considerably effective in practical use, particularly as a portable optical disc apparatus.
According to a 2nd aspect of the present invention, an optical disc apparatus which applies a light spot to an optical disc, thereby to record or reproduce information on or from the optical disc, comprises: first moving means for moving the light spot applied to the optical disc, in a radial direction of the optical disc; an optical head having converging means for converging the light spot on the optical disc; spot position detection means for generating a spot position signal which indicates a positional difference in a radial direction of the optical disc, between a center of the optical head and the light spot on the optical head; first control means for subjecting the spot position signal to a first processing by a spot position loop filter, and outputting the spot position signal to the first moving means; second moving means for moving the optical head in a radial direction of the optical disc; second control means for subjecting the spot position signal to a second processing by a traverse loop filter, and outputting the spot position signal to the second moving means; spot position signal monitoring means for receiving the spot position signal as an input, and outputting a first signal which indicates that the spot position signal comes to a value smaller than a prescribed value; and system operation control means for operating the first control means when the first signal is input, and operating the second control means after or simultaneously with the operation of the first control means. Therefore, the execution time for the spot position control precedent to the traverse control can be optimized and minimized, thereby realizing an optical disc apparatus which is considerably effective in practical use, particularly as a portable optical disc apparatus.
According to a 3rd aspect of the present invention, an optical disc apparatus which applies a light spot to an optical disc, thereby to record or reproduce information on or from the optical disc, comprises: first moving means for moving the light spot applied to the optical disc, in a radial direction of the optical disc; an optical head having converging means for converging the light spot on the optical disc; spot position detection means for generating a spot position signal which indicates a positional difference in a radial direction of the optical disc, between a center of the optical head and the light spot on the optical head; correction signal generation means for receiving the spot position signal as an input, and generating a correction signal for correcting the spot position signal; subtracting means for subtracting the correction signal from the spot position signal; second moving means for moving the optical head in a radial direction of the optical disc; and second control means for subjecting an output from the subtracting means to a processing by a traverse loop filter, and outputting the output to the second moving means. Therefore, the traverse control can be stabilized with a simple structure without using the spot position control, thereby realizing an optical disc apparatus which is considerably effective in practical use, particularly as a portable optical disc apparatus.
According to a 3rd aspect of the present invention, an optical disc apparatus which applies a light spot to an optical disc, thereby to record and reproduce information on or from the optical disc, comprises: first moving means for moving the light spot applied to the optical disc, in a radial direction of the optical disc; an optical head having converging means for converging the light spot on the optical disc; spot position detection means for generating a spot position signal which indicates a positional difference in a radial direction of the optical disc, between a center of the optical head and the light spot on the optical head; second moving means for moving the optical head in a radial direction of the optical disc; second control means for subjecting the spot position signal to a processing by a traverse loop filter, and outputting the spot position signal to the second moving means; and a coefficient multiplier for reducing a coefficient for the control by the second control means to a value smaller than that in a normal operation time, at starting of the operation of the second control means. Therefore, the traverse control can be stabilized with a simple structure without using the spot position control, thereby realizing an optical disc apparatus which is considerably effective in practical use, particularly as a portable optical disc apparatus.
According to a 5th aspect of the present invention, in the optical disc apparatus of the 1st or 2nd aspect, the first processing subjected by the first control means is a phase-lag compensation. According to the 5th aspect, the first processing to be performed to the spot position signal comprises only the phase-lag processing, i.e., low-band compensation processing, whereby the structure of the spot position filter can be simplified. Therefore, even when the self-weight dislocation occurs in the objective lens, the traverse control using the spot position signal can be performed with stability, or the execution time of the spot position control precedent to the traverse control can be optimized and minimized, thereby realizing an optical disc apparatus which is considerably effective in practical use, particularly as a portable optical disc apparatus.
According to a 6th aspect of the present invention, in the optical disc apparatus of the 5th aspect, the first processing subjected by the first control means includes compensation for reducing an open-loop gain at a primary resonance frequency of the first moving means, in addition to the phase-lag compensation. Therefore, even when the open-loop gain at the primary resonance frequency exceeds 0 dB, the phase margin can be secured and the spot position control is stabilized.
According to a 7th aspect of the present invention, in the optical disc apparatus of the 1st or 2nd aspect, the first processing subjected by the first control means is a phase-lead compensation and a phase-lag compensation, and the phase-lead compensation is started from a frequency lower than a primary resonance frequency of the first moving means. According to the 7th aspect, both of the phase-lead compensation and the phase-lag compensation, i.e., phase compensation and low-band compensation are performed as the first processing to be performed to the spot position signal. Accordingly, the oscillations can be suppressed in a low frequency band in the servo of the spot position control, according to the spot position signal having a sensitivity which cannot be increased. Therefore, even when the self-weight dislocation occurs in the objective lens, the traverse control using the spot position signal can be performed with stability, or the execution time for the spot position control precedent to the traverse control can be optimized and minimized, thereby realizing an optical disc apparatus which is considerably effective in practical use, particularly as a portable optical disc apparatus.
According to a 8th aspect of the present invention, an optical disc apparatus which applies a light spot to an optical disc, thereby to record or reproduce information on or from the optical disc, comprises: first moving means for moving the light spot applied to the optical disc, in a radial direction of the optical disc; an optical head having converging means for converging the light spot on the optical disc; spot position detection means for generating a spot position signal which indicates a positional difference in a radial direction of the optical disc, between a center of the optical head and the light spot on the optical head; tracking error detection means for generating a tracking error signal which indicates a positional dislocation between the light spot and a track on the optical disc; first control means for subjecting the spot position signal or the tracking error signal to a first processing by a phase compensation loop filter, and outputting the signal to the first moving means; second moving means for moving the optical head in a radial direction of the optical disc; second control means for subjecting the spot position signal to a second processing by a traverse loop filter, and outputting the signal to the second moving means; and system operation control means for operating the first control means to perform a phase-lag compensation and a phase-lead compensation by the phase compensation loop filter to the spot position signal, thereafter switching the spot position signal to the tracking error signal to perform the phase-lag compensation and the phase-lead compensation to the tracking error signal, and operating the second control means after operating the first control means. Therefore, even when the self-weight dislocation occurs in the objective lens, the traverse control using the spot position signal can be performed with stability. Besides, a loop filter can be commonly used for performing the phase-lead compensation and the phase-lag compensation in performing the spot position control and the tracking error control. Therefore, an optical disc apparatus which is considerable effective in practical use, particularly as a portable optical disc apparatus, can be obtained.